The estimation of the glomerular filtration rate (GFR) is an essential part of the evaluation of patients with chronic kidney disease (CKD). Recently, serum cystatin C has been proposed as a new endogenous marker of GFR. Authors compared serum creatinine, creatinine clearance calculated from Cockcroft and Gault formula and serum cystatin C against (51)CrEDTA clearance in 252 patients with CKD and GFR <90 mL/min/1.73 m(2). Analysis of correlations and diagnostic accuracy (receiver operating characteristic curves) of different GFR markers indicate that serum cystatin C is a more reliable marker of GFR in patients with CKD than serum creatinine.